The present invention relates generally to metal containers, and more particularly to metal cans.
Aluminum cans are used primarily as containers for retail sale of beverages in individual portions. Annual sales of such cans are in the billions and consequently, over the years, their design has been refined to reduce cost and improve performance. Other refinements have been made for ecological purposes, to improve reclamation and promote recycling.
Cost reductions may be realized in material savings, scrap reduction and improved production rates. Performance improvements may be functional in nature, such as better sealing and higher ultimate pressure capacity. Such improvements can allow the use of thinner sheet metal, which leads directly to material cost reductions. Performance improvements may also be ergonomic in nature, such as a can end configured to allow for easier pull tab access or better lip contact.
Aluminum cans are usually formed from a precoated aluminum alloy, such as the aluminum alloy 5182. The cans, which are typically made from relatively thin sheet metal, must be capable of withstanding pressures approaching 100 psi., with 90 psi being an industry recognized requirement. The cans are usually formed from a can body to which is joined a can lid or closure. Each of these components has certain specifications and requirements. For instance, the upper surface of the can lids must be configured to nest with the lower surface of the can bottoms so that the cans can be easily stacked one on top of the other. It is also desirable to have the can lids themselves nest with each other in a stacked arrangement for handling and shipping purposes prior to attaching the can lid to the can body. The ability to satisfy these functional requirements with the use of ever less material continues to develop.
A prior art disclosure, published under the Patent Cooperation Treaty in International Publication Number WO 96/37414, discloses can lid design for reduced metal usage and improved pressure capability. This can lid comprises a peripheral portion or xe2x80x9ccurl,xe2x80x9d a frustroconical chuckwall depending from the interior of the peripheral curl, an outwardly concave annular reinforcing bead or xe2x80x9ccountersinkxe2x80x9d extending radially inwards from the chuckwall, and a center panel supported by the inner portion of the countersink. The frustroconical chuckwall is inclined at an angle of between 20xc2x0 and 60xc2x0 with respect to an axis perpendicular to the center panel. A double seam is formed between this can end and a can body by a process wherein the peripheral curl is centered on the can body flange by a frustroconical/cylindrical chuck designed to fit into the frustroconical chuckwall of the can lid. The overlap of the peripheral curl on the lid with the can body flange is described to be by a conventional amount. Rotation of the can lid/can body, first against a seaming roll and then a flattening roll completes a double seam between the two parts. During the flattening operation, the portion of the chuckwall adjacent to the peripheral curl is bent to a cylindrical shape and flattened against the cylindrical surface of the chuck. The lid of International Publication Number WO 96/37414 incorporates known dimensions for the peripheral curl portion which is seamed to the can.
The can lid disclosed in International Publication Number WO 96/37414 requires a greater amount of metal than the can lid of the present invention, thereby increasing the manufacturing costs. The increased metal usage in this prior art stems from a higher, or deeper, countersink, a larger peripheral curl portion than is disclosed in the present invention and the use of a frustroconical chuckwall that is characterized by a single angle with respect to an axis perpendicular to the central panel. The can lid disclosed in WO 96/37414 is also susceptible to increased metal deformation during seaming and failure at lower pressures.
The present invention contemplates improved aluminum can lids combining a slanted chuckwall with a reduced seam. A preferred embodiment of the disclosed can lid has a center panel having a central axis that is perpendicular to a diameter of the outer rim of the can lid, an annular countersink extending radially outward from the center panel, an arcuate chuckwall extending radially outward from the annular countersink, a step portion, a transitional portion extending radially outward from the chuckwall, and a peripheral curl extending outwardly from the transitional portion. The step portion improves the consistency and integrity of a double seam formed between the can lid and the can body while the arcuate chuckwall improves the strength of the can lid as compared to a simple frustroconical chuckwall. These features reduce metal usage in manufacturing and are expected to reduce filled can failures, and allow the use of thinner sheet metal for the can lid.